Quantitative elucidation of in situ lithium metal anode modification on NCM811 cathode failure mechanisms in high-nickel solid-state lithium metal batteries

In SS-LMBs, uneven interfacial stress causes PC-NCM811 cathode failure, and the role of in situ Li metal anode modification in cathode degradation remains poorly understood. Herein, we systematically compared the electrochemical failure and thermal induction failure behaviors of PC-NCM811 for liquid LIBs, unmodified SSBs, and LiSn-LiF in situ modified SSLMBs (M-SSBs). The optimized anode generates a low-impedance, chemically stable solid–electrolyte interface (SEI), which effectively inhibits uncontrolled Li dendrite proliferation, alleviates accumulated internal stress, and blocks harmful byproduct migration. This design is expected to mitigate chemical cross-talk interference inside M-SSBs and induces the formation of an inorganic-rich, structurally robust cathode–electrolyte interface. Benefiting from stress regulation, the M-SSBs relieve cracks and preserve the NCM811 lattice integrity. It also delays irreversible phase transition by 20 °C and reduce exothermic enthalpy. This modification achieves favorable chemical–mechanical coupled regulation, which comprehensively suppresses the electrochemical deterioration and thermal degradation of PC-NCM811. It thus provides a feasible guideline for developing high-performance, thermally secure high-Ni SSLMBs.